Análise de novo implante ortopédico desenhado para proteção de partes moles na fixação das fraturas da ulna proximal: estudo comparativo in silico e in vitro

Abstract

Introduction: The treatment of multifragmentary fractures involving the metaphyseal region of the proximal ulna presents a significant challenge due to its complexity, high cost, and a high incidence of reoperations. This high rate of reoperations is primarily motivated by the need for implant removal, which frequently causes friction and discomfort in the soft tissues. Objective: This study aimed to introduce a novel orthopedic implant for the fixation of Type IIB proximal ulna fractures, designated as the Y-plate, specifically designed for soft tissue protection. Furthermore, it sought to compare its stability with three existing implants through a combined evaluation comprising in silico simulations, utilizing the Finite Element Method (FEM), and in vitro mechanical tests. Materials and Methods: The methodology initially involved the creation of 3D digital models of the PU from computed tomography (DICOM) images and modeling softwares (InVesalius®, Autodesk®MeshmixerTM, Rhinoceros®). This was performed in conjunction with four distinct plate and screw fixation systems (identified as A+B, Synthes®, LCP, and the Y-plate). Subsequently, the stability among these systems was compared through FEM simulations. The relative displacements of reference points, strategically located at the fracture ends, were evaluated under maximum loads at various elbow flexion angles (0°, 45°, and 90°), with applied forces of 50 N, 100 N, and 500 N. Bone displacement and implant stress were also assessed via visual analysis of color gradients and measurement of maximum von Mises stress.Following the in silico phase, in vitro tests were conducted using 3D-printed artificial bone models (polyamide material) and their corresponding metallic implants, simulating the identical fixation configurations examined in the computational study.Loads were applied to the specimens using an MTS universal testing machine. In both experimental approaches, the failure criterion parameter was defined as a displacement exceeding 2 mm between the reference points. For statistical calculations, analysis of variance (ANOVA) was employed, complemented by Tukey’s post-hoc test. Results: The results indicated that all fixation configurations demonstrated satisfactory stability in both studies, with displacements consistently below 2 mm. The A+B plate consistently exhibited the largest deviations across both simulations, whereas the Y-plate and Synthes® system demonstrated superior performance under diverse loading conditions, particularly evident in the in vitro study. Notably, when evaluating articular surface displacement (identified as the most critical parameter), the Y- plate showed superior performance compared to the other implants at 0º and 45º positions, and the second-best performance at 90º, thereby exceeding initial expectations and even its own in silico results. Localized concentrations of von Mises stresses were observed in both the Y-plate and A+B plate, yet these were accompanied by adequate safety coefficients. The results of Both in silico and in vitro studies unequivocally confirmed the efficacy of the tested systems. Conclusion: The novel implant offers stability equivalent to or superior to conventional implants, possessing distinctive advantages in soft tissue protection, potential to reduce costsand surgery time. This validates its foundational concept for subsequent stages of development and comprehensive clinical validation.